At the present time, most photovoltaic energy conversion devices, or solar cells, as they are also known, are constructed from the semiconducting material silicon. Such constructions are accomplished by the high temperature diffusion of suitable impurity atoms into a single crystal silicon base to produce a p-n junction near the surface of the base and in a plane parallel to said surface. Light incident on said diffused surface produces the photovoltaic effect--the direct conversion of light into electricity. Typically such diffusions are carried out at temperatures on the order of 1100.degree. C. The depth of the diffusion and the concentration of the diffused impourity atoms are determined by trade-offs between the sheet resistance of the diffused layer and the optical abosorption of the base material. Values of the junction depth and impurity atom profile will vary depending upon the particular material utilized for the base.
The primary problem that exists in using solar cells produced by this method for large-scale earth-based power systems has been the high cost of the cells. This high cost can be attributed to three factors: (1) the current low production rate of solar cells, (2) the complex processes involved in the production of the devices, and (3) the high cost of the single crystal semiconductor wafers used as the starting material for cell fabrication. At present, these factors combine to make the cost of solar cells approximately thirty times the cost which is generally considered to be necessary to make photovoltaic power supplies competitive with nuclear power.
It is therefore a primary object of the present invention to reduce the cost of photovoltaic devices by a simplification of the fabrication process, which will also permit the utilization of a lower cost starting material, such as polycrystalline material.
Other objects, features and advantages of the invention will become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.